Human to Animal Transmission of SARS-CoV-2
March 30, 2020 - 9 minutes readOne of the challenges we face right now is how little we know about the novel coronavirus SARS-CoV-2, which causes the illness COVID-19 in humans. Thanks to the work of scientists across the globe, our understanding is growing daily. In this post, we provide an update on our current knowledge around pets and SARS-CoV-2.
To date, there have been three reports of pets infected with SARS-CoV-2. We describe these in detail below, but first we want to explain the current state of testing for this virus because it is relevant for understanding what we know about these animal cases.
When you hear information in the news about the availability of test kits, these stories are referring to a specific technique called RT-PCR (Reverse Transcriptase Polymerase Chain Reaction) for detecting the genetic signature of viral particles in nasal mucus or saliva samples.
If the test is positive, meaning that the genetic code of the virus, called viral RNA, has been detected, then we know that the patient is infected whether or not they show any symptoms. Part of the reason that SARS-CoV-2 is spreading so rapidly is that people who seem perfectly healthy can infect others. For us to slow the spread of infection, we must increase RT-PCR testing dramatically (in addition to staying at home and maintaining social distance). This is the only way for us to identify infected individuals and quarantine them to keep others from being infected.
Among infected people, we observe huge variation in response to infection. Some people never show symptoms. Others have mild illness. Still others become severely ill and must be hospitalized. After a patient has recovered from COVID-19, another kind of test becomes relevant.
During the infection, the body mounts an immune response to fight the virus. This immune response includes producing antibodies against SARS-CoV-2. By taking a blood sample, we can carry out a different kind of test. Instead of analyzing genetic material, we look for the presence of these antibodies. When blood goes from not having antibodies to having these antibodies (reflecting the fact that the person has gone from not being infected to having been infected), this is called seroconversion, and it shows that the person has mounted an immune response to the virus.
Eventually, we should be able to conduct widespread blood tests, which will identify those individuals who have already made antibodies. Antibodies to viruses sometimes completely prevent future infection, and other times lessen the severity of future infection, but in either case, antibodies to viruses are helpful.
In addition to tests for the virus and for antibodies to the virus in people, some tests have also been carried out in pets. In Hong Kong, the government health service mandated that some pets of ill people be tested. This is where most of our information about pets and SARS-CoV-2 is coming from.
Three pets have tested positive for the presence of SARS-CoV-2. All of these animals (two dogs and a cat) were owned by people who were sick with COVID-19.
1. As we reported in our last blog post Dogs and COVID-19, a Pomeranian in Hong Kong tested positive for the presence of viral particles in its mouth and nose. It did not display signs of illness or active infection, and at that time, most veterinary professionals thought that it was possible that the dog had been contaminated through physical contact but was not necessarily actively infected. However, when a blood test was later performed, antibodies against SARS-CoV-2 were present in the dog’s blood. This indicates that the dog was infected with the virus. This dog, who was seventeen-years-old, has since passed away. Cause of death is unknown. The dog never displayed signs of illness.
*Source: Agriculture, Fisheries, and Conservation Department, Hong Kong
2. In a separate case in Hong Kong, two dogs from a home with an active human COVID-19 case were placed in quarantine and tested. One dog tested positive for the virus. The other did not. No blood test has been done at this time. The authorities in Hong Kong who detected these cases also tested seventeen dogs and eight cats from households with infected owners. All of these were negative.
*Source: MarketWatch
3. A cat in Belgium tested positive for SARS-CoV-2 in both saliva and feces. About a week after the cat’s owner began displaying symptoms of COVID-19, the cat displayed intestinal distress and breathing difficulties. It is important to keep in mind that this is the only case we know of, despite widespread presence of human infections around the world.
*Source: The Brussels Times
As far as we know, no human health authority in the United States is regularly testing the pets of ill people. However, in an attempt to assess more widespread infection in pets, two veterinary diagnostics companies tested thousands of dog and cat samples and did not detect any SARS-CoV-2 infections. However, we don’t have any information on whether or not the owners of these pets were infected. So while this is a reassuring finding in many ways, it does not give us an estimate of how likely it is for sick owners to transmit SARS-CoV-2 to their pets.
*Source: IDEXX Press Release, Antech Press Release
What does this all mean?
As scientists we are generally cautious about drawing conclusions from such little data, but here’s what we know. It appears possible for sick humans to transmit SARS-CoV-2 to dogs or cats, but at this point, this seems like a very rare occurrence. Like humans, infected pets may show little to no symptoms. We have no evidence that sick pets can transmit coronavirus to otherwise healthy, uninfected owners.
It’s also true that most viruses in the world “prefer” to infect one species over all others. Very few viruses are effective at infecting multiple species. Based on what we currently know, this is likely to remain true for SARS-CoV-2. It does a very good job of infecting people, getting into our bodies and our cells, and making us have some symptoms of disease. It does not do a similarly good job infecting dogs or cats. It seems that the virus may be able to get into dogs or cats in certain circumstances, and may even occasionally make them show signs of illness, but the very most important way this virus spreads is from person to person.
This last piece is crucial. Like you, we have heard reports of people abandoning their dogs because they are afraid that their dogs will make them sick. At this point, we have no evidence that this is possible or likely. We do not recommend abandoning dogs. The best thing we can do to keep our canine and human family members safe is to keep our pets with us and physically separated from other people or animals. If someone in your household does get sick, then they should try to stay separate from all other family members, including pets.
As we learn more, we will keep you informed, and your primary care veterinarian is always a good resource in these challenging times.